A highly trained operative known as Rei works for the Metropolitan Police Department’s Zero Section, a clandestine unit tasked with investigating closed cases that official channels cannot touch. Suffering from memory loss sustained during her training, Rei finds herself on two simultaneous paths: one is an external investigation into a human trafficking ring that preys on young women, and the other is an internal search for the fragments of her own forgotten past.

The case escalates dramatically when a group of rising terrorists seizes a classified and lethal killer virus, threatening to unleash it upon the population. In response, Public Security assigns a young specialist to assist with the investigation. Sarah Kodama, an expert in molecular biology and computer science, is sent to partner with Rei. However, the solitary and deeply mistrustful Rei refuses to work with her. Undeterred by Rei’s coldness, Sarah becomes intensely curious about the mysterious operative. She begins to dig into Rei’s history, eventually seeking out Asami, Rei’s former boss.

As Sarah digs deeper into the secrets of the Zero Section, she uncovers a conspiracy far larger than a simple terrorist plot. The man who appears before her is not an ally but an assassin with a mission to destroy the Zero Section entirely. The investigation forces Rei to confront the gaps in her memory, which are intrinsically linked to the very criminals she is hunting and the shadowy organization she works for. As the terrorists announce their deadline for the attack, Rei must protect the inquisitive Sarah, stop the release of the virus, and finally uncover the truth hidden within her own lost memories.